Aleph transformer noise.

[a007udio]

I have build dual mono Aleph amplifier and have problem with transformers noise.
The noise comes from the transformers and not from the speakers, amplifier sounds wonderfull. If i disconnect amplifier board from PSU the noise disappear.
Each channel draws approximately 130 watts and i have 300VA transformer per channel.
I load the transformer with 160w on another PSU and resistors and it was silent.
Any advice what to check?

 

[Zen Mod]

pics

 

[a007udio]

The amplifier is made in two enclosures:
First are transformers with soft start and diode bridge. The right transformer on the picture was replaced for test purposes.
Second is the capacitor bank, amplifier and speaker protection.

 

[rayma]

Each of the two transformers makes mechanical noise?

 

[a007udio]

Yes, even if i disconnect one of them from amplifier, both of them making noise.

 

[rayma]

Do any other amplifiers make similar noises?

 

[a007udio]

No, i use f5 turbo and some comercial amplifiers and the transformers are silent.

 

[rayma]

Have you tried removing the mounting bolts and setting the transformers on insulating pads,
to see if the noises are gone?

You are not using the mounting kits supplied with the toroids, a large rubber washer on each side of the toroid,
and then a large steel washer on top. The mounting bolts look very small also. Have you tried that?

 

[ticknpop]

Try Quasimodo CRC snubbbing. It reduced/eliminated the noise in a few Torroids I had noise issues with.

 

[RS232]

Have a service note for a commercially build amplifier regarding this same issue and the solution for it (well for this one) is swapping one of the wires going to the bridge rectifiers.
Give it a go simple and cheap to check.

 

[alwaysHiFi]

Your mains supply voltage? Rated input voltage of transformer? Hz?

If you remove one transformer and power it up with no load. Does it make noise? Can measure current at primary with no load, should be low mA AC say below 20mA. To check that transformer is happy and not having to high of input voltage. (Using care mains voltages)

What is your soft start? Is it switching over to full mains voltage? Pure sine wave?

 

[a007udio]

Yesterday i tried different mounting methods and five different transformers. With all the transformers problem is the same.
Mains voltage is 235V and the primar voltage is 235V.

Today i load (102W) the power supply after diode bridge with resistors and with this configuration the transformer is silent.

 

[a007udio]

This is test with power supply from another project. Silent.
Next, i will try this power supply with Aleph.

 

[Zen Mod]

try adding some caps locally in xformers case

you're routing non-filtered DC from bridges to filter in remote case - it can be cause of ringing

generally, when doing as you did - say in case of CRC filter, first C must be in primary case, with xformers

then umbilical is acting as part of R, with final (R)C in case with amp

 

[a007udio]

Ok, i will try to add some capacitance after the diodes. Tnx.
Below is a picture of another silent setup.

 

[Zen Mod]

conditions are simply not same

OK to confirm that xformer itself isn't POS, but you have different problem in your setup

 

[osscar]

I once had it - 500VA transformer hum even without load..noise disappeared when the rating of the primary side fuse was increased from 3A and 5A

 

[a007udio]

Yes, i know that conditions are different, i just want to eliminate the problems step by step.
Some time ago i owned Musical Fidelity Nu-Vista integrated amplifier with separate power supply. There were only transformers in that enclosure.
Anyway, adding 40000uF of capacitance after diodes unfortunately didn't make any difference.

 

[Zen Mod]

then you have something wrong in amp case

can't see that you have it that way, try making CRC if you have just C filter

how you arranged connection between safety gnd and audio gnd?

it's enough and just right to have it ditto in xformer case

 

[RS232]

Have you tried different rectifiers ?
Or apply caps to the rectifiers terminals some of then generate RF.